This invention relates to the production of tantalum, niobium and other metal powders and their alloys by the reduction of the corresponding metal oxide with gaseous active metals such as Mg, Ca and other elemental and compound reducing materials, in gaseous form.
Tantalum and niobium are members of a group of metals that are difficult to isolate in the free state because of the stability of their compounds, especially some of their oxides. A review of the methods developed to produce tantalum will serve to illustrate the history of a typical manufacturing process for these metals. Tantalum metal powder was first produced on a commercial scale in Germany at the beginning of the 20th Century by the reduction of the double salt, potassium heptafluorotantalate (K2TaF7) with sodium. Small pieces of sodium were mixed with the tantalum containing salt and sealed into a steel tube. The tube was heated at the top with a ring burner and, after ignition, the reduction proceeded quickly down the tube. The reaction mixture was allowed to cool and the solid mass, consisting of tantalum metal powder, unreacted K2TaF7 and sodium, and other products of the reduction was removed by hand using a chisel. The mixture was crushed and then leached with dilute acid to separate the tantalum from the components. The process was difficult to control, dangerous, and produced a coarse, contaminated powder, but nevertheless pointed the way to what became the principal means of production of high purity tantalum in later years.
Commercial production of tantalum metal in the United States began in the 1930""s. A molten mixture of K2TaF7 containing tantalum oxide (Ta2O5) was electrolyzed at 700xc2x0 C. in a steel retort. When the reduction was completed, the system was cooled and the solid mass removed from the electrolysis cell, and then crushed and leached to separate the coarse tantalum powder from the other reaction products. The dendritic powder was not suitable for use directly in capacitor applications.
The modern method for manufacturing tantalum was developed in the late 1950""s by Hellier and Martin (Hellier, E. G. and Martin, G. L., U.S. Pat. No. 2,950,185, 1960). Following Hellier and Martin, and hundreds of subsequently described implementations or variations, a molten mixture of K2TaF7 and a diluent salt, typically NaCl, is reduced with molten sodium in a stirred reactor. Using this system, control of the important reaction variables, such as reduction temperature, reaction rate, and reaction composition, was feasible. Over the years, the process was refined and perfected to the point where high quality powders with surface area exceeding 20,000 cm2/gm are produced and materials with surface area in the 5000-8000 cm2/gm range being typical. The manufacturing process still requires the removal of the solid reaction products from the retort, separation of the tantalum powder from the salts by leaching, and treatments like agglomeration to improve the physical properties. Most capacitor grade tantalum powders are also deoxidized with magnesium to minimize the oxygen content (Albrecht, W. W., Hoppe, H., Papp, V. and Wolf, R., U.S. Pat. No. 4,537,641, 1985). Artifacts of preagglomeration of primary particles to secondary particle form and doping with materials to enhance capacitance (e.g. P, N, Si, and C) are also known today.
While the reduction of K2TaF7 with sodium has allowed the industry to make high performance, high quality tantalum powders thus, according to Ullmann""s Encyclopedia of Industrial Chemistry, 5th Edition, Volume A 26, p. 80, 1993, the consumption of tantalum for capacitors had already reached a level of more than 50% of the world production of tantalum of about 1000 tons per annum, whereas there had essentially been no use of niobium for capacitors, even through the raw material base for niobium is considerably broader than that for tantalum and most of the publications on powder preparation and capacitor manufacturing methods mention niobium as well as tantalum.
Some of the difficulties of applying that process to niobium are as follows:
While the manufacturing process of the type shown in Hellier and Martin (U.S. Pat. No. 2,950,185) for the reduction of potassium heptaflorotantalate by means of sodium in a salt melt is available in principle for the production of high purity niobium powders via potassium heptafluoroniobate, it doesn""t work well in practice. This is due, in part, to the difficulty of precipitating the corresponding heptafluoroniobate salts and is due, in part, to the aggressively reactive and corrosive nature of such salts, such that niobium produced by that process is very impure. Further, niobium oxide is usually unstable. See, e.g., N. F. Jackson et al, Electrocomponent Science and Technology, Vol. 1, pp. 27-37 (1974).
Accordingly, niobium has only been used in the capacitor industry to a very minor extent, predominantly in areas of with lower quality requirements.
However, niobium oxide dielectric constant is about 1,5 times as high as that of a similar tantalum oxide layer, which should allow in principle, for higher capacitance of niobium capacitors, subject to considerations of stability and other factors.
As for tantalum itself, despite the success of the K2TaF7/sodium reduction process, there are several drawbacks to this method.
It is a batch process subject to the inherent variability in the system; as a result, batch to batch consistency is difficult. Post reduction processing (mechanical and hydro-metallurgical separations, filtering) is complex, requiring considerable human and capital resources and it is time consuming. The disposal of large quantities of reaction products containing fluorides and chlorides can be a problem. Of fundamental significance, the process has evolved to a state of maturity such that the prospects for significant advances in the performance of the tantalum powder produced are limited.
Over the years, numerous attempts were made to develop alternate ways for reducing tantalum and similar metal compounds, including Nb-compounds, to the metallic state (Miller, G. L. xe2x80x9cTantalum and Niobium,xe2x80x9d London, 1959, pp. 188-94; Marden, J. W. and Rich, M. H., U.S. Pat. No. 1,728,941, 1927; and Gardner, D., U.S. Pat. No. 2,516,863 1946; Hurd, U.S. Pat. No. 4,687,632). Among these were the use of active metals other than sodium, such as calcium, magnesium and aluminum and raw materials such as tantalum pentoxide and tantalum chloride. As seen in Table I, below, the negative Gibbs free energy changes indicate that the reduction of the oxides of Ta, Nb and other metals with magnesium to the metallic state is favorable; reaction rate and method determine the feasibility of using this approach to produce high quality powders on a commercial scale. To date, none of these approaches were commercialized significantly because they did not produce high quality powders. Apparently, the reason these approaches failed in the past was because the reductions were carried out by blending the reducing agents with the metal oxide. The reaction took place in contact with the molten reducing agent and under conditions of inability to control the temperature of highly exothermic reactions. Therefore, one is unable to control morphology of the products and residual reducing metal content.
The use of magnesium to deoxidize or reduce the oxygen content of tantalum metal is well known. The process involves blending the metal powder with 1-3 percent magnesium and heating to achieve the reduction process. The magnesium is in the molten state during a portion of the heating time. In this case, the objective is to re-move 1000-3000 ppm oxygen and only a low concentration of MgO is produced. However, when a much greater quantity of tantalum oxide is reduced a large quantity of magnesium oxide is generated. The resulting mixture of magnesium, tantalum oxide and magnesium oxide can under conditions of poorly controlled temperature, form tantalum-magnesium-oxygen complexes that are difficult to separate from the tantalum metal.
It is a principal object of the invention to provide a new approach to production of high performance, capacitor grade tantalum and niobium powders that provides a means of eliminating one or more, preferably all, the problems of traditional double salt reduction and follow on processing.
It is further object of the invention to enable a continuous production process.
It is a further object of the invention to provide improved metal forms.
Another object is to provide niobium/tantalum alloy powders of capacitor grade quality and morphology.
We have discovered that the prior art problems can be eliminated when metal oxides such as Ta2O5 and Nb2O5 and suboxides in massive amounts are reduced with magnesium in gaseous form, substantially or preferably entirely. The oxide source should be substantially or preferably entirely in solid. The oxide is provided in the form of a porous solid with high access throughout its mass by the gaseous reducing agent.
The metals that can be effectively produced singly or in multiples (co-produced) through the present invention are in the group of Ta, Nb, and Ta/Nb alloy, any of these alone or with further inclusion of added or co-produced Ti, Mo, V, W, Hf and/or Zr. The metals can also be mixed or alloyed during or after production and/or formed into useful compounds of such metals. The respective stable and unstable oxide forms of these metals can be used as sources. Metal alloys may be produced from alloyed oxide precursors, e.g. resulting from coprecipitation of a suitable precursor for the oxide.
Vapor pressures of some of the reducing agents are given as follows:
The temperature of reduction varies significantly depending on the reducing agent used. The temperature ranges for reduction of (Ta, Nb) oxide are: with Mg(gas)xe2x88x92800-1,100xc2x0 C., Al(gas)xe2x88x921,100-1,500xc2x0 C., Li(gas)xe2x88x921,000-1,400xc2x0 C., Ba(gas)xe2x88x921,300-1,900xc2x0 C.
Different physical properties as well as morphology of the metal powder produced by reduction can be achieved by variations of temperature and other conditions of processing within the effective reduction range.
One embodiment of the invention includes a first step of reducing an oxide source of selected metal(s) substantially to free 80-100% (by weight) of the metal values therein as primary powder particles, then leaching or other steps of hydrometallurgy to separate the metal from residual reducing agent oxide and other byproducts of the reduction reaction and from residual condensed reducing agent (optionally), followed by one or more deoxidation steps under less concentrated reagent conditions than in the first gross reduction step (and with better tolerance of molten state of the reducing agent), then further separation as might be needed.
In accordance with this first embodiment the invention provides for a single stage reduction process for the production of metal powders as cited above, comprising the steps of:
(a) providing an oxide or mixed oxides of the metal(s), the oxide itself being in a form that is traversable by gas,
(b) generating a gaseous reducing agent at a site outside the oxide mass and passing the gas through the mass at an elevated temperature,
(c) the reactants selection, porosity of the oxide, temperature and time of the reduction reaction being selected for substantially complete reduction of the oxide(s) to free the metal portion thereof, the residual oxide of reducing agent formed in the reaction being easily removable,
whereby a high surface area, flowable metal powder is formed in a process that essentially avoids use of molten state reducing agent in production of metal or alloy powder.
Preferred reducing agents used in this reduction process of the first embodiment are Mg, Ca and/or their hydrides. Particularly preferred is Mg.
Preferred is the production of Nb and/or Ta metals, optionally alloyed with each other and/or with alloying elements, selected from the group consisting of Ti, Mo, W, Hf, V and Zr.
A second embodiment of the invention provides for a two-stage reduction process, comprising the steps of:
(a) providing an oxide or mixed oxide of the metal(s), the oxide being in a form that is traversible by gas,
(b) passing a hydrogen containing gas, alone or with gaseous diluent, through the mass at an elevated temperature in a manner for partial reduction of the oxide(s),
(c) the porosity of the oxide, temperature and time of reduction reaction being selected to remove at least 20% of the oxygen contained in the oxide to produce a suboxide,
(d) reducing the suboxide with reducing metal(s) and/or hydrides of one or more reducing metals, thereby substantially completely reducing the oxide to free the metal portion thereof.
Preferrably the reducing metals and/or metal hydrides are brought into contact with the suboxide in gaseous form.
Preferred reducing metals in the second reduction step of this second embodiment are Mg and/or Ca and/or their hydrides. Particularly preferred is Mg.
Reduction temperature preferably (for Mg) is selected between 850xc2x0 C. up to normal boiling point (1150xc2x0 C.)
The process according to the present invention (both embodiments) specifically has been developed to provide capacitor grade tantalum and niobium and tantalum nio-bium alloy powders and Ta/Nb materials or application of equivalent purity and/or morphology needs. The greatest gap of the state of the art is filled in part by the availability of capacitor grade niobium enabled by this invention, but a segment of the tantalum art is also enhanced thereby. In all cases the tantalum and/or niobium may be enhanced by alloying or compounding with other materials during the reduction reaction production of the tantalum/niobium or thereafter. Among the requirements for such powders is the need for a high specific surface presintered agglomerate structure of approximately spherical primary particles which after pressing and sintering results in a coherent porous mass providing an interconnected system of pore channels with gradually narrowing diameter to allow easy entrance of the forming electrolyte for anodization and manganese nitrate solution [Mn(NO3)2] for manganization.
The reduction of oxides with gaseous reducing agents at least during the initial reduction phase allows for easy control of temperature during reduction to avoid excessive presintering. Furthermore, as compared to prior art proposals using liquid reducing metals, the controlled reduction with gaseous reducing metals does not lead to contamination of the reduced metal with the reducing metal by incorporation into the reduced metal lattice. It has been found that such contamination mainly occurs during the initial reduction of (in case of Nb) Nb2O5 to NbO2. This at first appeared surprising because niobium suboxide (NbO2) contains only 20% less oxygen than niobium pentoxide (NbO2.5). This effect was traced back to the fact that the suboxide forms a considerably more dense crystal lattice than the pentoxide. The density of NbO2.5 is 4.47 g/cm3, whilst that of NbO2 is 7.28 g/cm3, i.e., the density is increased by 1.6 times by the removal of only 20% of the oxygen. Taking into account the different atomic weights of niobium and oxygen, a reduction in volume of 42% is associated with the reduction of NbO2.5 to NbO2. Accordingly, Applicants state (without limiting the scope of the invention thereby) that the effect according to the invention can be explained in that during the reduction of the pentoxide magnesium in contact with the oxide is able to diffuse relatively easily into the lattice, where it has a high mobility, whereas the mobility of magnesium in the suboxide lattice is significantly reduced. Accordingly, during the reduction of the suboxide the magnesium substantially remains on the surface and remains accessible to attack by washing acids.
This even applies in case of a controlled reduction with gaseous magnesium. Obviously in this case reduction occurs also during the critical initial reduction to suboxide only at the surface of the oxide, and magnesium oxide formed during reduction does not enter the oxide or suboxide powder. Preferred temperature during reduction with magnesium gas is between 900 and 1100xc2x0 C., particularly preferred between 900 and 1000xc2x0 C.
Temperature may be increased up to 1200xc2x0 C. after at least 20% of the oxygen is removed to improve presintering.
The reduction of the pentoxide with hydrogen produces a suboxide which is already sintered with the formation of agglomerates comprising stable sintered bridges, which have a favorable structure for use as a capacitor material.
Lower temperatures necessitate longer times of reduction. Moreover, the degree of sintering of the metal powders to be produced can be adjusted in a predeterminable manner by the choice of reduction temperature and reduction time. The reactors are preferably lined with molybdenum sheet or by a ceramic which is not reduced by H2, in order to prevent contamination.
Furthermore, the reduction time and reduction temperature should be selected so that at least 20% of the oxygen is removed from the pentoxide. Higher degrees of reduction are not harmful. However, it is generally not possible to reduce more than 60% of the oxygen within practicable time scales and at tolerable temperature.
After a degree of reduction of 20% or more has been reached, the suboxide is present. According to this process embodiment the reduction product is preferably still held (annealed) for some time, most preferably for about 60 to 360 minutes, at a temperature above 1000xc2x0 C. It appears that this enables that the new, dense, crystal structure can be formed and stabilized. Since the rate of reduction decreases very considerably with the degree of reduction, it is sufficient to heat the suboxide at the reduction temperature under hydrogen, optionally with a slight decrease in temperature. Reduction and annealing times of 2 to 6 hours within the temperature range from 1100 to 1500xc2x0 C. are typically sufficient. Moreover, reduction with hydrogen has the advantage that impurities such as F, Cl and C, which are critical for capacitor applications, are reduced to less than 10 ppm, preferably less than 2 ppm.
The suboxide is subsequently cooled to room temperature ( less than 100xc2x0 C.) in the reduction apparatus, the suboxide powder is mixed with finely divided powders of the reducing metals or metal hydrides and the mixture is heated under an inert gas to the reduction temperature of the second stage. The reducing metals or metal hydrides are preferably used in a stoichiometric amount with respect to residual oxygen of the acid earth metal suboxide, and are most preferably used in an amount which is slightly in excess of the stoichiometric amount.
One particularly preferred procedure consists of using an agitated bed in the first stage and of carrying out the second stage, without intermediate cooling, in the same reactor by introducing the reducing metals or metal hydrides. If magnesium is used as the reducing metal, the magnesium is preferably introduced as magnesium gas, since in this manner the reaction to form metal powder can readily be controlled.
After the reduction whether according to the one-stage or to the two-stage reduction process to metal is complete, the metal is cooled, and the inert gas is subsequently passed through the reactor with a gradually increasing content of oxygen in order to deactivate the metal powder. The oxides of the reducing metals are removed in the manner known in the art by washing with acids.
Tantalum and niobium pentoxides are preferably used in the form of finely divided powders. The primary grain size of the pentoxide powders should approximately correspond to 2 to 3 times the desired primary grain size of the metal powders to be produced. The pentoxide particles preferably consist of free-flowing agglomerates with average particle sizes of 20 to 1000 xcexcm, including a specific preference of a narrower range of most preferably 50 to 300 xcexcm particle size.
Reduction of niobium oxide with gaseous reducing agents can be conducted in an agitated or static bed, such as a rotary kiln, a fluidized bed, a rack kiln, or in a sliding batt kiln. If a static bed is used, the bed depth should not exceed 5 to 15 cm, so that the reducing gas can penetrate the bed. Greater bed depths are possible if a bed packing is employed through which the gas flows from below. For tantalum, preferred equipment choices are described in Example 2 and the paragraph between Examples 2 and 3, below, with reference to FIGS. 1-4.
Niobium powders which are particularly preferred according to the invention are obtained in the form of agglomerated primary particles with a primary particle size of 100 to 1000 nm, wherein the agglomerates have a particle size distribution as determined by Mastersizer (ASTM-B822) corresponding to D10=3 to 80 xcexcm, particularly preferred 3 to 7 xcexcm, D50=20 to 250 xcexcm, particularly preferred 70 to 250 xcexcm, most preferably 130 to 180 xcexcm and D90 =30 to 400, particularly preferred 230 to 400 xcexcm, most preferably 280 to 350 xcexcm. The powders according to the invention exhibit outstanding flow properties and pressed strengths, which determine their processability to produce capacitors. The agglomerates are characterized by stable sintered bridges, which ensure a favorable porosity after processing to form capacitors.
Preferably niobium powder according to the invention contains oxygen in amounts of 2500 to 4500 ppm/m2 surface and is otherwise low in oxygen, up to 10,000 ppm nitrogen and up to 150 ppm carbon, and without taking into account a content of alloying metals has a maximum content of 350 ppm of other metals, wherein the metal content is mainly that of the reducing metal or of the hydrogenation catalyst metal. The total content of other metals amounts to not more than 100 ppm. The total content of F, Cl, S is less than 10 ppm.
Capacitors can be produced from the niobium powders which are preferred according to the invention, immediately after deactivation and sieving through a sieve of mesh size 400 xcexcm. After sintering at a pressed density of 3,5 g/cm3 at 1100xc2x0 C. and forming at 40 V these capacitors have a specific capacitance of 80,000 to 250,000 xcexcFV/g (as measured in phosphoric acid) and a specific leakage current density of less than 2 nA/xcexcFV. After sintering at 1150xc2x0 C. and forming at 40 V, the specific capacitor capacitance is 40,000 to 150,000 xcexcFV/g with a specific leakage current density of less than 1 nA/xcexcFV. After sintering at 1250xc2x0 C. and forming at 40 V, capacitors are obtained which have a specific capacitor capacitance (as measured in phosphoric acid) of 30,000 to 80,000 xcexcFV/g and a specific leakage current density of less than 1 nA/xcexcFV.
The niobium powders which are preferred according to the invention have a BET specific surface of 1.5 to 30 m2/g, preferably of 2 to 10 m2/g.
Surprisingly it has been found that capacitors can be made from Nb/Ta-alloy powders in way that the capacitors have an appreciably higher specific capacitance obtained from capacitors made from pure Nb-and pure Ta-powers or anticipated for an alloy be simple linear interpolation. Capacitances (xcexcFV) of capacitors with sintered Nb-powder anodes and sintered Ta-powder anodes having the same surface area are approximately equal. The reason is that the higher dielectric constant of the insulating niobium oxide layer (41 as compared to 26 of tantalum oxide) is compensated by the larger thickness of the oxide layer per volt (anodization voltage) formed during anodization. The oxide layer thickness per volt of Nb is about twice as thick as that formed on Ta (about 1.8 nm/V in the case of Ta and about 3.75 nm/V in the case of Nb). The present invention can provide a surface related capacitance (xcexcFV/m2) of alloy powder capacitors which is up to about 1.5 to 1.7 higher than the expected value from linear interpolation between Nb powder capacitors and Ta powder capacitors. This seems to indicate that oxide layer thickness per volt of anodization voltage of alloy powders of the invention is closer to that of Ta, whereas the dielectric constant of the oxide layer is closer to that of Nb. The foregoing surprisingly high capacitance of the alloy may be associated with a different structural form of oxide of alloy components compared to structure of oxides on surfaces of pure Nb powders. Indeed, preliminary measurements have revealed that oxide layer growth of a 15 at.-%Taxe2x80x9485 at.-% Nb alloy is almost 2.75 nm/volt.
The present invention accordingly further comprises an alloy powder for use in the manufacture of electrolyte capacitors consisting primarily of niobium and containing up to 40 at.-% of tantalum based on the total content of Nb and Ta. Alloy powder in accordance with the present invention shall mean that the minor Ta-component shall be present in an amount greater than the amount of ordinary impurity of niobium metal, e.g. in an amount of more than 0.2% by weight (2000 ppm, corresponding to 2 at.-% for Ta).
Preferrably, the content of Ta is at least 2 at.-% of tantalum, particularly preferred at least 5 at.-% of tantalum, most preferably at least 12 at.-% of tantalum, based on the total content of Nb and Ta.
Preferably the content of tantalum in the alloy powders in accordance with the invention is less than 34 at.-% of tantalum. The effect of capacitance increase is gradually increasing up to a ratio of Nb- to Ta-atoms of about 3. Higher than 25 at.-% Ta based on the total content of Nb and Ta does only slightly further increase the effect.
The alloy powders according to the invention preferably have BET-surfaces multiplied with the alloy density of between 8 and 250 (m2/g)xc3x97(g/cm3), particularly preferred between 15 and 80 (m2/g)xc3x97(g/cm3). The density of the alloy material may be calculated from the respective atomic ratio of Nb and Ta multiplied by the densities of Nb and Ta respectively.
The effect of capacitance increase of alloying is not limited to powders having the structure of agglomerated spherical grains. Accordingly the alloyed powders in accordance of the invention may have a morphology in the form agglomerated flakes preferably having have a BET-surface times density of between 8 and 45 (m2/g)xc3x97(g/cm3).
Particularly preferred alloy powders are agglomerates of substantially spherical primary particles having a BET-surface times density of 15 to 60 (m2/g)xc3x97(g/cm3). The primary alloy powders (grains) may have mean diameters of between 100 to 1500 nm, preferrably 100 to 300 nm. Preferrably the deviation of diameter of primary particles from mean diameter is less than a factor 2 in both directions.
The agglomerate powders may have a mean particle size as determined in accordance with ASTM-B 822 (Mastersizer) as disclosed for niobium powders above.
Particularly preferred alloy powders have a ratio of Scott density and alloy density of between 1.5 and 3 (g/inch3)/(g/cm3).
Any production method known in the art for the production of capacitor grade tantalum powder may be used, provided that a precursor is used which is an alloyed precursor containing niobium and tantalum approximately at the atomic ratio of Nb and Ta desired in the metal powder alloy instead of precursor containing tantalum alone.
Useful alloy precursors may be obtained from coprecipitation of (Nb,Ta)-compounds from aqueous solutions containing water soluble Nb- and Ta-compounds e.g. coprecipitation of (Nb, Ta)-oxyhydrate from aqueous solution of heptafluoro-complexes by the addition of ammonia and subsequent calcination of the oxhydrate to oxide.
Flaked powders may be obtained by electron beam melting of a blend of high purity tantalum and niobium oxides, reducing the molten ingot, hydriding the ingot at elevated temperature, and comminuting the brittle alloy, dehydriding the alloy powder and forming it into flakes. The flakes are thereafter agglomerated by heating to 1100 to 1400xc2x0 C. in the presence of a reducing metal such as Mg, optionally with doping with P and/or N. This process for the manufacture of xe2x80x9cingot derivedxe2x80x9d powder is generally known from U.S. Pat. No. 4,740,238 for the production of tantalum flaked powder and from WO 98/19811 for niobium flaked powder.
Particularly preferred Nb-Ta-alloy powders having the morphology of agglomerated spherical grains are produced from mixed (Nb, Ta)-oxides by reduction with gaseous reducing agent as described herein.
The metal powders produced are suitable for use in electronic capacitors and other applications including, e.g. the production of complex electro-optical, superconductive and other metal and ceramic compounds, such as PMN structures and high temperatures form metals and oxide.
The invention comprises the said powders, the methods of producing such powders, certain derivative products made from such powders and methods for making such derivative products.
The capacitor usage can be accompanied by other known artifacts of capacitor production such as doping with agents to retard sinter densification or otherwise enhance end product capacitance, leakage and voltage breakdown.
The invention enables several distinct breakthroughs in several of its various fields of application.
First, the well known high performance tantalum powders for making computer/telecommunications grade solid electrolyte, small size capacitors (high capacitance per unit volume and stable performance characteristics) can now be made with substantial net savings of cost, complexity and time.
Second, other reactive metalsxe2x80x94especially Nb and alloys, e.g. Taxe2x80x94Nb, Taxe2x80x94Ti, Nbxe2x80x94Ti, can be introduced as replacement for Ta in capacitors in certain applications with a cost saving or as replacement for the high end Al market with much better performance, particularly enabling much smaller sizes for equivalent capacitance and use of solid electrolyte. Commercial aluminum electrolytic capacitors use wet electrolyte systems.